Spray deposition of CuInS2 on electrodeposited ZnO for low-cost solar cells

CuInS2 (CIS) thin films are deposited using chemical spray pyrolysis on top of a single (compact) and a double (compact + porous) ZnO film obtained by electrodeposition by changing the composition, pH and temperature of the bath. Conductive glass has been used as primary substrate. CIS films are deposited at 300 °C and using N2 as carrier. A buffer layer of TiO2 is incorporated by spray to protect the ZnO layer against dissolution during the subsequent spraying of CIS. Relevant properties, such as morphology, composition and thickness are evaluated using SEM, EDX and XRD. Also, UV-Vis analyses are carried out to assess the band gap value of CIS, resulting in 1.42 eV. Carrier densities and flat band potentials (Vfb) are calculated from Mott-Schottky plots. The values of Vfb are 0.70, 1.10 and 0.42 V for TiO2, ZnO and CIS respectively. I-V curves in the dark and under illumination prove that the materials can be combined to obtain solar cells. The dark response for the two devices built with single and double layers of ZnO is very similar, showing diode behavior with good rectification ratios. Under illumination, the presence of the porous ZnO improves the performance of the cell, as reflected by the higher values of photocurrent and open circuit potential.